EGU2010-4962 Double-Difference relocation and focal mechanisms of Lucanian Apennine (southern ) seismicity.

Cosmiana Maggi (1,2)*, Alberto Frepoli (1), Giovanni Battista Cimini (1), Rodolfo Console (1,2), Massimo Chiappini (1)

(1) - Istituto Nazionale di Geofisica e Vulcanologia (INGV), via di Vigna Murata, 605, 00143, Rome, Italy; (2) – Centro di Geomorfologia Integrata per l’Area del Mediterraneo (CGIAM), , Italy.

14˚ 15˚ 16˚ 17˚ 18˚ 19˚ Top of layer Velocity of model 42˚ 42˚ 1646 1 1223 Depth Magnitude Gargano (km) Test8 (km/s) Molise 1627 T T Introduction 1456 Mattinata fault Data and analysis Group 3 (brown) Group 4 (green) 1805 Tavoliere 0 4.27 ADRIATIC Foggia 346 Ofanto Graben SEA The Lucanian Apennine belongs to the southern Apenninic 1349 Barletta-Bisceglie We studied the seismicity occurred in the period 2001-2008 analyzing a -2 5.52 This group is located in the area between 40.44°-40.57°N of latitude and 15.50°-16.00°E of longitude named -Pietrapertosa and consists of 67 This seismicity is located within the area of Auletta Basin, Vallo di Diano and Val d’Agri (40.10°-40.43° N of latitude and 15.62°-16.10°E of longitude). It consists of 78 earthquakes (Fig.3). We P P 1560 Hystorical seismicity 1688 1731 Canosa 1456 Bari 1732 1930 1456 earthquakes (Fig.3). We relocated 64 events with the double-difference method improving the hypocentral locations (Fig.10, 11). Large part of relocated 74 events with the double-difference method improving hypocentral locations (Fig.13, 14). Events are mainly localized within the 9-15 km depth range (Fig.13g, h). Hypocenter are more Ofanto River high-quality waveform dataset collected during two recent passive 1702 989 A P U L IA -11 6.1 chain which is located within the complex, articulated Campania XI X - IX VIII UF B R A D A N O F O R E D E E Murge 41˚ 41˚ MAF F O R E L A N D a) b) Napoli VF IrF 1851 seismic experiments carried out in the study region (Fig. 2). The earthquakes show hypocentral depths between 10 and 18 km (Fig.10g, h). These relocated events are elongated in a E-W direction (Fig.11a, b). A new clustered by using HypoDD code. We can identify one main cluster to the SE of the upper Val d’Agri active faults. This includes events of a significant swarm named Moliterno (February-December AnIrF -23 6.5 central Mediterranean plate boundary zone between the Bradano River 1694 Potentino L U C A N AI N EV: 020531 1632 SGF result in this work is given by the seismic sequence of November 2008, which consists of 33 events (1.0 ≤ ML ≤ 2.9). The increased number of seismic 2002; Fig.14b, d, e, f). The relocated events of the Moliterno swarm show hypocenter depths between 6 and 11 km. To the East and the NE of the Moliterno swarm the microseismicity is rather 1980 Irpinia SAPTEX array (green circles in Fig.2) was a long-term tomography -35 7.31 Z= 10.18 km Eurasian and African plates. The geodynamic setting of this Salerno AlF Gulf Murge Francavilla P Tarantine Fontana 1561 1857 Taranto Otranto Channel stations in the study area, with the temporary array of the passive experiment SeSCAL, give us the occasion to relocate these events with good accuracy. sporadic. It is worth to note that the upper Val d’Agri was hit by the strong 1857 earthquake with ground motion reached intensity XI in the localities of , Grumento and . VDF VAF A P E N N NI E experiment lasted from June 2001 to December 2004 (Cimini et al., -45 7.9 region is characterized by the NNW-SSE relative plate Vallo di Diano Salento Moliterno 2 Moliterno 3 MMFS Agri Valley This cluster is oriented along a NW-SE direction (Fig.11a, b) and shows a depth range of 10-17 km (Fig.11c, d). Cilento MAIF Nardo’ 1836 2006), while the SeSCAL array (magenta triangles in Fig.2) has operated convergence between Eurasia and Africa. The tectonics of 1743 Table I: Lucanian Apennines velocity Pietrapertosa 1 60 HypoEllipse MaF TARANTO HypoEllipse HypoDD HypoDD 40˚ 40˚ 8 TYRRHENIAN MeF Pollino Range GULF model computed with VELEST code 50 the Lucanian Apennine is accommodated by the collision SEA Policastro CiF in the period between December 2007 and March 2009. From the 40.6 Abriola- 40.6 Abriola- T Auletta Basin P T P T Gulf PF CaF (Maggi et al., 2009). 1 Auletta Basin Sibari 20 30 Pietrapertosa Pietrapertosa T 6 40 Plain continuous recordings of the temporary stations we extracted over 15600 15˚ 16˚ 17˚ 40.55 40.55 40.4 40.4 between the Adria microplate and the Apenninic belt. 1836 Tavoliere P 30 1184 P 25 40.5 40.5 2 4 3 waveforms of events with local magnitude range 1.5 ≤ ML ≤ 4.1. These 15

Lat N Lat 20 1854 Recent geodetic data suggest that the Adria is a microplate N Lat 1857 Numbereventsof 20 Numbereventsof 1857 1870 1638 IONIAN SEA 2 EV: 070727 0304 Thrust front Normal faults 40.45 40.45 a) b) EV: 080405 1657 10 40.3 Val d’Agri 40.3 Val d’Agri 1 Sila were hand-picked along with those recorded by the permanent stations of Adriatic Sea separated from the Eurasian and African plates, while its Strike-slip faults 10 15 Z= 9.99 km Z= 12.94 km 1638 1832 40.4 Vallo Vallo 39˚ 39˚ 40.4 0 0 T a) 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 di Diano 2 14˚ 15˚ 16˚ 17˚ 18˚ 19˚ the Italian National Seismic Network (RSNC; white squares in Fig.2) 10 MaxErr_H(km) b) MaxErr_H(km) N Lat di Diano southern border is ambiguously defined. The eastward 40.35 40.35 N Lat Numbereventsof Numbereventsof 5 Fig.1: Southern Italy historical and instrumental seismicity map. Historical seismicity from 15.5 15.6 15.7 15.8 15.9 16 b)15.5 15.6 15.7 15.8 15.9 16 P 20 40.2 40.2 Fig.15: Composite focal mechanisms computed for four obtaining a dataset of 15666 P- and 9228 S-arrival times. We located 566 5 a) P 60 migration of the extension-compression system of the the Catalogo parametrico dei terremoti italiani (CPTI Working Group, 2004). Instrumental Murge Lon E Lon E T clusters located in the Moliterno area (see Fig.14b,d). 0 0 15 50 seismicity from the Seismicity map of Italy, 2000-2007, INGV-CNT, Roma, (Castello et al., 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 HypoEllipse HypoDD events out of 1047 recorded earthquakes using the Hypoellipse code a) b) MaxErr_H(km) Apenninic chain is related to the subduction process of the 41˚ 41˚ MaxErr_H(km) c) d) 40 40.1 2008). Active faults from Galadini et al. (2000), Maschio et al. (2005) and Papanikolaou and 0 0 40.1 Apulia foreland 12 40 10 Adria microplate lithosphere and the opening of the Roberts (2007) (from Frepoli et al., 2010). (Lahr, 1989), the 1D velocity model and Vp/Vs ratio of 1.83 computed Bradano foredeep EV: 081120 2125 30 Irpinia 35 a) 10 Z= 13.77 km 20 15.7 15.8 15.9 16 b) 15.7 15.8 15.9 16 16.1 Numbereventsof for the study region by Maggi et al. (2009) (Table I). Taking into account 30 1 5 Numbereventsof Lon E Tyrrhenian back arc basin. Since the Early Pleistocene, the 8 -10 -10 10 Lon E Potentino 25 Pietrapertosa 2 HypoEllipse HypoDD the hypocentral distribution, we subdivided the studied region into 6 Lucanian Appenines 2 0 0 active extension within the chain produced a broad and Murge 6 20 c) 0 1 2 3 4 5 6 7 8 9 10 11 12 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 Err_Z (km) d) Err_Z (km) 1857 0 1857 15 -20 -20 0 sub-areas (Fig. 3). We relocated the seismicity of each sub-area using the Salerno Gulf tarantine 4 T 7 20

complex system of NW-trending normal faults and related Numbereventsof Pietrapertosa Numbereventsof 10 P 2 Adriatic Sea 2 Depth (km) 6 double-difference (DD) technique (HypoDD code, Waldhauser and 5 3 basins. Seismological data and recent geodetic studies Depth (km) -30 -30 5 15 -10 -10 0 0 Moliterno c) 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 Ellsworth, 2000; Waldhauser, 2001). This algorithm can be used when Cilento Err_Z (km) d) Err_Z (km) 4 reveal that the Apenninic chain is undergoing a NE-trending 10 EV: 0111121 0621 1 Taranto Gulf 7 -40 -40 3 the hypocentral distance between two earthquakes is small compared to 12 Z= 11.54 km 2 -20 -20

extension, with seismic deformation rates higher in the 6 Numbereventsof Numbereventsof Castelluccio 15.5 15.6 15.7 15.8 15.9 16 5 Depth (km) 10 Lon E Depth (km) 5 d) 1 southern portion. The southern Apenninic chain is one of the source receiver distance and the scale length of velocity 40˚ 40˚ 15.5 15.6 15.7 15.8 15.9 16 8 c) Lon E 0 0 Policastro 4 Fig.12: Composite focal mechanisms computed e) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 -30 heterogeneity. Therefore the ray paths between the events and common Pollino Range HypoDD rms (s) f) rms (s) -30 the main seismically active regions of Italy (Fig.1). In the Gulf 3 6 for five clusters located in the Pietrapertosa area HypoDD 20 35 (see Fig.11b,d). 15.7 15.8 15.9 16 16.1 station are similar and the difference in the travel times for two events Tyrrhenian Sea 2 4 15.7 15.8 15.9 16 d) last four centuries, this area was characterized by moderate Numbereventsof 0 30 c) Lon E Numbereventsof 15 Lon E Ionian Sea 1 2 0 25 HypoDD Tyrrhenian Sea recorded by the same station can be attributed only to the spatial offset Sibari Plain HypoDD to strong events. Among the strongest earthquakes 0 0 -10 20 Ionian Sea e) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.05 0.1 0.15 0.2 0.25 0.3 km rms (s) f) 10 supported by historical records, the 1694 events (Me = 6.9) between the events. We computed composite focal mechanisms using the rms (s) -10 15 1857 1857 Fig.14 (left side): Map view of the hypocentral 25 35 Fig.13 (right side): Rms residuals (seconds), 0 10 0 distribution and W-E cross-sections of the 74 events Numbereventsof FPFIT code (Reasenberg and Oppenheimer, 1985) only for the relocated 0 50 -20 horizontal and vertical errors (kilometres) and Numbereventsof 5 30 5 hit the Irpinia area and the 1857 earthquake (Me 20 -20 located with Hypoellipse (a, c) and HypoDD code (b, 15˚ 16˚ 17˚ depth distribution of the 74 earthquakes located -10 25 Depth (km) 0 0 -10 d). 3D plots of events relocated with = 6.9) hit the upper Val d’Agri and Vallo di Diano area, both events grouped in clusters characterized by a maximum of 2 km of Fig.3: Map with the Hypoellipse location of the 566 earthquakes. Colours are indicating the six groups of -30 using Hypoellipse (a, c, e, g) and HypoDD code g) 0 5 10 15 20 25 30 5 10 15 20 25 15 Depth (km) Depth of events (km) h) Depth of events (km) double-difference method (e, f). Red dotted line trace 20 -30 (b, d, f, h). distance between the hypocenters. events analyzed with HypoDD. -20 variation in seismogenic base. Brown line shows the with effects of the XI degree on the 10 15 -20

-40 Depth (km) Depth (km) active structures observed in this area (DISS Working 10 30 Numbereventsof Numbereventsof -40 Mercalli–Cancani–Sieberg (MCS) scale. The least strong 5 16 15.6 12 Group, 2009). Blue star: epicentres of historical 5 40.6 15.8 15.8 -30 40.5 40.4 15.6 16 40.4 40.5 40.6 25 -30 earthquakes. Yellow circle outlines cluster of the Lon E f) Lon E 10 0 0 Lat N 16.1 40.4 earthquake in this region hit the Irpinia area in 1980 (Ms = Fig.2: Seismic stations used in this study. White squares indicate the permanent stations of the Potentino 1 Potentino 2 Potentino 3 5 10 15 20 25 30 35 40 e) Lat N 16 15.7 Moliterno sequence. Numbers indicate clusters used g) 5 10 15 20 25 30 35 20 40.4 40.3 15.815.9 15.8 15.9 40.2 Group 2 (red) Depth of events (km) h) Depth of events (km) 8 40.2 40.1 15.7 f) 16 Italian national network, green circles indicate the temporary stations deployed for the T P Fig.11: Map view of the hypocentral distribution and W-E cross-sections of the 64 events located with e) Lat N Lon E 16.1 to compute composite focal mechanisms. 6.9) with effects of the X degree MCS and normal T 15 Lon E Lat N SAPTEX array (June 2001 – December 2004) and magenta triangles indicate the temporary T Fig.10: Rms residuals (seconds), maximum horizontal (MaxErr_H) and vertical (Err_Z) errors (kilometres) 6 P Hypoellipse (a, c) and HypoDD code (b, d). 3D plots of events relocated with double-difference method (e, f). stations deployed for the SeSCAL project (December 2007 – March 2009) (from Frepoli et This group is located in the Potentino area (15.42-15.88 E, 40.5-40.9 N) mechanism of rupture. and depth distribution of the 64 earthquakes located with Hypoellipse (a, c, e, g) and HypoDD code (b, d, f, Red dotted line trace variation in seismogenic base. Yellow circle outlines the cluster of the 4 10 HypoEllipse HypoDD Numbereventsof al., 2010). P Numbereventsof and consists of 89 events located with Hypoellipse (Fig.3). 84 are the T h). Abriola-Pietrapertosa sequence. Numbers indicate clusters used to compute composite focal mechanisms. 40.9 40.9 P 2 5 Group 6 (blue) Apulia foreland Apulia foreland b) relocated earthquakes with HypoDD code. Most earthquakes are located a) 0 0 Bradano foredeep Bradano foredeep 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 40.8 40.8 EV: 081108 0924 EV: 080721 1223 EV: 080514 1629 a) MaxErr_H(km) b) MaxErr_H(km) Seismicity of this group is located in the area of the Bradano within the 7-20 km depth range (Fig.7g, h). Hypocentral locations are Z= 10.38 km Z= 19.61 km Z= 18.33 km 40.7 Matera Group 1 (yellow) Group 5 (magenta) 25 40.7 15 Foredeep and the Apulia Foreland (40.40°-40.90° N of Lat N Lat Irpinia 1 Irpinia 2 Irpinia 3 N Lat Matera improved with the double-difference method: vertical and horizontal Potentino 4 Potentino 5 Castelluccio 1 40.6 This seismicity is located in the Irpinia region within an area stretching from Seismicity of this group is concentrated between 39.62°-40.14° N of latitude 20 latitude, 16.00°-16.88°E of longitude). It consists of 56 40.6 errors and rms are reduced (Fig.7); hypocenters are more clustered (Fig.8). 40.5 T 10 15 40.5 T P P and 15.65°-16.36°E of longitude in the area of the Mercure Valley and the 40.62º to 40.90º of latitude N and from 15.10º to 15.54º of longitude E (Fig.3). T T T T earthquakes (Fig.3). This area is characterized by a more Analyzing the epicentral distribution we observe that the earthquakes are P 40.4 This group consists of 102 events located with Hypoellipse code. Event P Pollino Range. It consists of 54 earthquakes (Fig.3). The microseismicity of Fig.18 (left side): Composite focal 10 sparse seismicity. From historical records we know that this 16 16.2 16.4 16.6 16.8 16 16.2 16.4 16.6 16.8 P 5 Numbereventsof mainly located to the SW of the two Potentino sequences of 1990 and mechanism computed for one cluster Numbereventsof Lon E Lon E P P 5 hypocentres are concentrated between 10 and 18 km of depth (Fig.4g, h). T this group is located in the same area of the small 1998 seismic sequence of located in the Castelluccio area (see area was not hit by strong earthquakes. We relocated 54 1991 (Fig.8a, b). A small seismic sequence started with the event of April a) b) HypoEllipse HypoDD fig.17b, d). 0 0 Hypocentral errors and rms are significantly reduced using the EV: 040904 0236 EV: 080225 0542 Castelluccio. We relocated 50 events with the double-difference method 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 events with the double-difference method improving the 0 0 18, 2002 (ML = 4.1), located at 12.4 km of depth beneath Savoia di c) Err_Z (km) d) Err_Z (km) Z= 12.48 km Z= 18.77 km double-difference method (Fig.4). In this way hypocenters are more clustered improving hypocentral locations (Fig.16, 17). Hypocenters are more 8 hypocentral locations (Fig.19, 20). Most of the -10 -10 EV: 050917 0044 EV: 070607 1716 EV: 070718 1041 12 Lucania, is placed to the SW of the grouped area (Fig.8a, b). Hypocentral 7 (Fig.5). Analyzing the epicentral distribution we observe that the events are Z= 17.09 km Z= 5.61 km Z= 10.57 km concentrated in the 10-15 km depth range (Fig.16g, h). There is a gap of microseismicity is located in the Bradano foredeep area. To -20 -20 depth of this sequence is ranging between 8 and 13 km (Fig.8c, d). Fig.9: Composite focal mechanisms computed for seven clusters located in the Potentino area (see EV: 020713 0557 6 10 Fig.8b, d). 5 8 -30 -30 Depth (km) microseismicity in the 23-32 km depth range (Fig.17). Few events are deeper Depth (km) mainly located between the structures of the 1980 Irpinia earthquake (main Fig.6: Composite focal mechanisms computed for three clusters located in the Irpinia HypoEllipse HypoDD the west, close to the eastern margin of the chain, the Moreover, this cluster is slightly elongated in a NW-SE direction (Fig.8f). Z= 19.61 km 4 area (see Fig.5b, d). 6 -40 -40 fault and antithetic; Fig.5a, b). The HypoDD hypocenters show shallower 40.9 than 30 km. This deep seismicity is located to the SW of the Pollino Range 3 seismicity shows hypocentral depths between 9 and 30 km, 40.9 4

Numbereventsof -50 2 Numbereventsof -50 depths in comparison with those obtained with Hypoellipse. Moreover, depth and could be related with the Southern Tyrrhenian Subduction Zone. while in the eastern part of the Bradano foredeep it is 16 16.1 16.2 16.3 16.4 16.5 16.6 16.7 16.8 16.9 16 16.1 16.2 16.316.4 16.5 16.6 16.716.8 16.9 12 30 1 2 Lon E HypoEllipse HypoDD Lon E is increasing from NW to SE (Fig.5c, d, e, f). HypoEllipse HypoDD 40.8 0 0 characterized by deeper events (9-40 km depth range) 10 25 40.8 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 HypoDD e) rms (s) f) rms (s) HypoDD 41 8 20 40.1 (Fig.20). We observe a cluster of shallow events (around 5-8 41 40.1 15 0 25 4 1991 7 70 40 1998 1 12 6 15 1991 40.7 3 km of depth) to the east of Matera city. The deep crustal 0 -10 60 40.7 6 40 40 10 20 1998 Pollino 10 N Lat 1990 40.9 40.9 1864 4 1990 N Lat 5 30 Pollino Mercure 10 seismicity in the Bradano Foredeep and the Apulia Foreland -10 -20 Numbereventsof 50 Numbereventsof Savoia di Lucania 2 Mercure Range 8 1864 5 Potenza Range 39.9 1853 2 5 Potenza 4 39.9 Policastro Policastro 15 1853 Valley 6 -20 -30 Lat N Lat 40 40.6 40.6 Gulf Valley N Lat area indicates the westward flexure of the Adria plate 2 20 Gulf 0 0 3 Depth (km) 1980 a) 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 1 4 5 -40 10 30 40.8 3 b) 39.8 -30 40.8 1980 MaxErr_H(km) MaxErr_H(km) 39.8 Numbereventsof beneath the Apenninic belt. Numbereventsof Lat N Lat Lat N Lat

2 Depth (km) Numbereventsof

Numbereventsof 10 20 20 2 -50

Numbereventsof -40 5 Numbereventsof 15 40.5 40.5 1 39.7 Fig.20 (right side): Map view of hypocentral distribution and W-E cross-sections of the 50 events 16 39.7 0 0 10 1 0 5 10 15 20 25 30 35 40 45 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 -50 16.2 40.7 40.7 0 0 g) Depth of events (km) Depth of events (km) located with HypoEllipse (a, c) and HypoDD code (b, d). 3D plots of the events relocated with the 16.4 15 a) 15.5 15.6 15.7 15.8 15.9 b) 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 h) 40.9 16.8 16.6 0 0 15.5 15.6 15.7 15.8 a) b) MaxErr_H(km) 15.8 15.9 16 16.1 16.2 16.3 15.6 15.7 16 16.1 16.2 16.3 double-difference method (e, f). Red dotted line trace variation in seismogenic base. Yellow circle 40.7 16.4 16.6 40.7 40.9 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 MaxErr_H(km) a) 15.7 b) 15.8 15.9 Fig.19: Rms residuals (seconds), horizontal and vertical errors (kilometres) and depth distribution of the 50 40.5 16.2 16.8 a) b) 10 Lon E Lon E Lon E Lon E Lat N 16 Lon E Lon E 40.5 MaxErr_H(km) MaxErr_H(km) 10 outlines the cluster of Matera. Lat N 10 HypoEllipse HypoDD 15 HypoEllipse HypoDD earthquakes located with Hypoellipse (a, c, e, g) and HypoDD code (b, d, f, h). 25 100 40.6 40.6 0 8 0 References 15.1 15.2 15.3 15.4 15.5 5 0 0

a) b)15.1 15.2 15.3 15.4 15.5 Numbereventsof 5 20 Numbereventsof 1991 80 Lon E Lon E 1991 10 1998 1998 Castello, B., Moschillo, R., Pignone, M., Vinci, S., Doumaz, F., Nostro, C., Selvaggi, G., 2008. Seismicity map of Italy, -5 -5 6 -10 -10 HypoEllipse 1 1 2000-2007. INGV-CNT, Roma. HypoDD 0 15 60 0 1 2 3 4 5 6 7 8 9 10 0 -10 -10 Conclusions 0 1853 0 1853 1864 c) Err_Z (km) d) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 4 4 -20 Cimini, G.B., De Gori, P. and Frepoli, A., 2006. Passive seismology in Southern Italy: the SAPTEX array. Annals of 1864 2 Err_Z (km) 1990 5 -20 Geophysics , 49 (2/3), 825-840.

-15 3 Numbereventsof 10 40 20 1990 -15 5 Numbereventsof 3 2 2 -30 8 -30 The accurate earthquake relocations performed with the double-difference method in this study allow us to retrieve a very detailed CPTI Working Group, 2004. Catalogo Parametrico dei Terremoti Italiani, versione 2004 (CPTI04), INGV, Bologna.

Numbereventsof 1980

Numbereventsof 1980 -20 -10 -20 5 20 -10 7 0 0 http://emidius.mi.ingv.it/CPTI04/ 15 Depth (km)

0 1 2 3 4 5 6 7 8 9 0 0.5 1 1.5 2 2.5 3 3.5 Depth (km) 6 Depth (km) d) -40 picture of the microseismicity in the area of the Lucanian Apennine. Earthquakes are mostly located along the Apenninic chain and -25 Depth (km) c) Err_Z (km) Err_Z (km) -40 1 -25 DISS Working Group, 2009. Database of Individual Seismogenic Sources (DISS), Version 3.1.0: A compilation of 0 0 5 6 c) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 d) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 10 -30 potential sources for earthquakes larger than M 5.5 in Italy and surrounding areas. http://diss.rm.ingv.it/diss/, © INGV Err_Z (km) Err_Z (km) -20 -20 4 -30 10 -50 -50 overlaps the area characterized by the great active normal faults of the Southern Apennines (Group1, Group2). The studied 2009 - Istituto Nazionale di Geofisica e Vulcanologia - All rights reserved. Depth (km) 5 Depth (km) 3 20 -35 Numbereventsof

2 Numbereventsof 5 -35 8 microseismicity beneath the chain could be explained with the post-seismic relaxation process related to the 1980 strong Irpinia Frepoli, A., Maggi, C., Cimini, G.B., Marchetti, A., Chiappini, M., 2008. Seismotectonic of Southern Apennines from 10 4 15.7 15.8 15.9 16 16.1 16.2 16.3 d)15.6 15.7 15.8 15.9 16 16.1 16.2 16.3 recent passive seismic experiments, Journal of Geodynamics, doi:10.1016/j.jog.2010.02.007 -30 1 c) 15.5 15.6 15.7 15.8 15.9 c) -30 d) 6 Lon E 15 Lon E 15.5 15.6 15.7 15.8 3 Lon E earthquake (Group1), the 1990 and 1991 Potentino sequences (Group2) and the 1998 Castelluccio sequence (Group 5). The 8 0 0 e) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 Lon E HypoDD Galadini, F., Meletti, C. and E. Vittori, 2000. Stato delle conoscenze sulle faglie attive in Italia: elementi geologici di rms (s) f) HypoDD HypoDD 15.1 15.2 15.3 15.4 15.5 rms (s) HypoDD 2 4 superficie. In: Galadini et al., Editors, Le ricerche del GNDT nel campo della pericolosità sismica (1996–1999), 6 c) seismicity beneath the outer margin of the chain, in the Bradano Foredeep area (Group 6), is more scattered. The depth of the CNR-Gruppo Nazionale per la Difesa dai Terremoti, Roma, pp. 107–136 Also available from Numbereventsof 10 Lon E 20 30 Numbereventsof -40 1 2 0 http://www.ingv.it/gndt/Pubblicazioni/Meletti_copertina.htm. 4 d) 0 0 15.1 15.2 15.3 15.4 15.5 25 1998 seismogenic layer is around 20 km beneath the Apenninic chain and between 30 and 40 km below the outer margin of the chain and Numbereventsof Numbereventsof 5 15 0 0 0 1998 -10 Lahr, J.C., HYPOELLIPSE/Version 2.0: a computer program for determining local earthquake hypocentral parameters, 2 HypoDD 1991 e) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 f) 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 HypoDD 20 rms (s) rms (s) -10 the Apulia Foreland. This eastward deepening indicates a deeper boundary between the brittle and ductile crust beneath the external magnitude, and first motion pattern. U. S. Geol. Surv. Open File Rep., 95, 89-116, 1989. -10 1991 -20 0 0 10 15 Maggi, C., Frepoli, A., Cimini, G. B., Console, R., Chiappini, M., 2009. Recent seismicity and crustal stress field in the 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 1864 1990 -10 20 15 -20 e) rms (s) f) rms (s) 1853 1864 margin of the Lucanian Apennine and the foredeep, compared to that beneath the chain itself. This increasing seismogenic layer depth Lucanian Apennines and surroundings areas (Southern Italy): seismotectonic implications. Tectonophysics, 463, 0 1853 -30 10 -20 130-144, doi:10.1016/j.tecto.2008.09.032.

25 Numbereventsof 5 Numbereventsof 1990 25 -20 15 -30 0 5 -40 is associated with the westward flexural bending of the Adriatic continental lithosphere beneath the Apenninic chain. The available 10 Depth (km) Maschio, L., Ferranti L. and P. Burrato, 2005. Active extension in Val d’Agri area, southern Apennines, Italy:

1980 Depth (km) 20 -10 1980

Depth (km) implications for the geometry of the seismogenic belt, Geophys. J. Int., 162, pp. 591–609 20 -30 Depth (km) -40 0 0 10 composite focal mechanisms computed in this study suggest that the whole Southern Apennines are characterized by a NE-trending -10 g) 0 5 10 15 20 25 30 0 5 10 15 20 25 30 -30 -50 15 Depth of events (km) h) Depth of events (km) Papanikolaou I.D. and G.P. Roberts, Geometry, 2007. Kinematics and deformation rates along the active normal fault 15 -20 5 -50

Numbereventsof system in the soutern Apennines: implications for fault growth, J. Struct. Geol., 29, pp. 166–188. Fig.7: Rms residuals (seconds), horizontal and vertical errors (kilometres) and depth distribution of the 84 Numbereventsof 5 15.6 extensional stress regime in agreement with previous studies. The more constrained locations of microseismicity examined in this 10 10 40.8 16.2 15.8 -20 earthquakes located using Hypoellipse (a, c, e, g) and HypoDD code (b, d, f, h). 15.5 40.8 16 16 40 Reasenberg, P., and D. Oppenheimer, 1985. FPFIT, FPPLOT and FPPAGE: FORTRAN computer programs for Depth (km) -30 15.8 15.6 e) 40 39.8 15.8 f) 16.2 39.8 Numbereventsof Numbereventsof 40.6 15.7 study is a further contribution to the comprehension of the seismogenesis and state of stress of a tectonically complex region as the e) Lat N 15.6 15.7 40.6 0 0 15.6 Lat N calculating and displaying earthquake fault-plane solutions, U.S. Geol. Surv. Open-File Rep. 85-739, 1985. 5 5 15.5 f) 15.8 0 5 10 15 20 25 30 35 40 45 50 Lat N Lon E Lon E Lon E g) 0 5 10 15 20 25 30 35 40 45 50 Depth (km) Fig.5 (left side): Map view of hypocentral distribution and W-E cross-sections of the 97 events located with Lon E Lat N Depth of events (km) h) Depth of events (km) -30 Southern Apennines characterized by a very high seismic hazard. Moreover, the scarce microseismicity observed in some sectors Waldhauser, F., 2001. HypoDD: A program to compute double-difference hypocenter locations, U.S. Geol. Surv. Open 0 0 -40 Hypoellipse (a, c) and HypoDD code (b, d). 3D plots of events relocated with double-difference method (e, Fig.17: Map view of the hypocentral distribution and W-E cross-sections of the 50 events located with g) 0 5 10 15 20 25 h) 0 5 10 15 20 25 30 35 Fig.8: Map view of hypocentral distribution and W-E cross-sections of the 84 events located with Hypoellipse File Rep., 01-113. Depth of events (km) Depth of events (km) 41 41 f). Red dotted line trace variation in seismogenic base. Brown lines: active structures observed in this area (a, c) and HypoDD code (b, d). 3D plots of events relocated with double-difference method (e, f). Green stars Fig.16: Rms residuals (seconds), maximum horizontal (MaxErr_H) and vertical (Err_Z) errors Hypoellipse (a, c) and HypoDD code (b, d). 3D plot of the events located with double-difference method (e, f). -40 along the Apenninic chain could be related with active fault segments presently locked where possible large earthquakes might be Fig.4: Rms (seconds), Maximum Horizontal (MaxErr_H) and vertical (Err_Z) errors (kilometres) and depth 40.8 15.5 40.8 (DISS Working Group, 2009). Blue stars are epicentres of historical earthquakes and green stars are (kilometres) and depth distribution of the 50 earthquakes located using Hypoellipse (a, c, e, g) and HypoDD Red dotted line trace variation in seismogenic base. Grey line: coastline. Yellow star: epicentres of historical Waldhauser, F., and W.L. Ellsworth, 2000. A double-difference earthquake location algorithm: Method and application 15.3 15.4 hypocentre of hystorical earthquakes. Red dotted line trace variation in seismogenic base. Yellow circle outlines to the northern Hayward Fault, California, Bull. Seismol. Soc. Am., 90, 1353-1368. Lat N 40.6 15.2 15.1 15.2 distribution of the 97 best earthquakes located using Hypoellipse (a, c, e, g) and HypoDD code (b, d, f, h). 15.1 15.3 15.4 15.5 40.6Lat N hypocentres. Numbers indicate clusters used to compute composite focal mechanisms. the Savoia di Lucania cluster. Numbers indicate clusters used to compute composite focal mechanisms. code (b, d, f, h). earthquakes. Numbers indicate clusters used to compute composite focal mechanisms. expected in the future. e) Lon E f) Lon E Corrisponding author. E-mail address: [email protected] (Cosmiana Maggi).